This invention relates in general to a web cleaning system and more specifically, to an apparatus and process for cleaning flexible webs.
In the art of electrophotography an electrophotographic member comprising a photoconductive insulating layer on a conductive layer is imaged by first uniformly electrostatically charging the imaging surface of the photoconductive insulating layer. The member is then exposed to a pattern of activating electromagnetic radiation such as light, which selectively dissipates the charge in the illuminated areas of the photoconductive insulating layer while leaving behind an electrostatic latent image in the non-illuminated area. This electrostatic latent image may then be developed to form a visible image by depositing finely divided electroscopic toner particles on the surface of the photoconductive insulating layer. The resulting visible toner image can be transferred to a suitable receiving member such as paper. This imaging process may be repeated many times with reusable photoconductive insulating layers.
The electrophotographic member is often in the form of a flexible multilayered photoreceptor belt comprising a substrate, a conductive layer, an optional hole blocking layer, an optional adhesive layer, a charge generating layer, and a charge transport layer and, in some embodiments, an anti-curl backing layer.
Although excellent toner images may be obtained with multilayered belt photoreceptors, it has been found that as more advanced, higher speed electrophotographic copiers, duplicators and printers were developed, the electrical and mechanical performance requirements have become more demanding. Moreover, new digital color products could not tolerate coating defects at the size levels previously found acceptable for light lens copiers. It has also been found that these electrical and mechanical performance requirements were not being met because of defects in one or more of the coated layers of the multilayered belt photoreceptors. These defects are caused by the presence of dirt particles on the substrate, conductive layer, optional hole blocking layer, optional adhesive layer, charge generating layer, charge transport layer and/or optional anti-curl backing layer. Thus for example, particles of dirt (particulate debris) residing on an uncoated or coated substrate surface during application of coatings to form an electrostatographic imaging member, such as a photoreceptor, can cause bubbles or voids to form in the various applied coating layers. It is believed that the dirt particles behave in a manner similar to a boiling chip that initiates solvent boiling at the location of the particle. This local boiling problem is aggravated when a coating solution is maintained near the boiling point of the coating solvent during deposition of the coating or during drying. The formation of bubbles in a coating is particularly acute in photoreceptor charge generation layer coatings and in charge transport layer coatings. Also, dirt particles tend to trap air during application of a coating and the trapped air expands during drying to form an undesirable bubble in the coating.
Further, any dirt particles residing on one or both major surfaces of an electrophotographic imaging member web substrate or coating thereon can adversely affect adjacent surfaces when the web is rolled up into a roll because the dirt particles cause impressions on the adjacent web surfaces. Because these undesirable impressions can be repeated through more than one overlapping web layer, large sections of a coated web must be scrapped. Where large belts, e.g. ten pitch belts, are to be fabricated, a 10 percent defect rate for a single pitch can result in the discarding of 60 to 70 percent of the entire web because very large expanses of defect free surfaces are required for such large belts.
The sources of the dirt particles include transporting systems, coating systems, drying systems, cooling systems, slitting systems, winding systems, unwinding systems, debris from the electrophotographic imaging member web substrate itself, workers, and the like.
In relatively thin charge blocking layers, such as organopolysiloxane layers applied with a gravure coater, any dirt particles present on the web surface tends to lift the coating layer and cause local coating voids. This also occurs with relatively thin adhesive layers between a charge blocking layer and a charge generation layer. Usually, after a web substrate is coated with the charge blocking layer and adhesive layer, the coated web substrate is rolled up into a roll and transported to another coating station. During unrolling or unwinding of the coated web, static electricity is generated as the outermost ply of the coated web is separated from the roll. This static electricity tends to attract dirt particles to the exposed surfaces of the web.
It has been found that brushing, buffing or other cleaning systems which physically contact the delicate and fragile surfaces of a coated or uncoated electrophotographic imaging member web substrate can cause undesirable scratches in the delicate outer surface of the substrate even if the contact systems are employed in conjunction with electrostatic discharge bars. Cleaning systems that do not contact the coated or uncoated electrophotographic imaging member web substrate, such as air knives and vacuum systems, whether or not assisted with electrostatic discharge bars, are not capable of removing small particles, those having an average particle size of less than about 100 micrometers to 30 micrometers range due to electrostatic attraction and a thin protective inertial air boundary layer on the substrate surface.
The use of a contact cleaner roll making continuous rolling contact with a moving web can remove loose particles of contamination from the web, if the outer surface of the roll has a tacky outer surface. As the web moves over the cleaner roll, the loose particulate matter is transferred from the web to the contact cleaner roll. As this transfer process continues, the transferred contaminants accumulate on the surface of the cleaner roll. The cleaner roll itself eventually becomes contaminated and looses its effectiveness to the point where it can redeposit undesirable particles on a web during the cleaning operation. Thus, the cleaner roll is replaced or cleaned periodically to restore its effectiveness. This is typically accomplished by shutting down the system or process, retracting the cleaner roll, and washing and drying it manually. Attempts to clean these rolls by hand encountered difficulties because the rolls were normally in inaccessible locations. Further, cleaning of the entire outer periphery of a contact cleaning roll required scrubbing of the entire outer peripheral of the contact cleaning roll with cleaning material. Since contact cleaning rolls are mechanically driven, these rolls could not be easily rotated for cleaning unless they are separated from the driving device or removed entirely from the cleaning module. To avoid down time of the system or process, these contact cleaner rolls can be cleaned without interrupting the continuous movement of web through the apparatus by a device for sequential cleaning of the contact cleaner rolls. This type of contact cleaner roll system is disclosed, for example, in U.S. Pat. No. 5,251,348, the disclosure thereof being incorporated herein in its entirety.
When a web coating system utilizes contact cleaning rolls for cleaning a web of one type carrying durable strongly adhering coatings, the same coating system can not be utilized for processing other types of coating operations where the web contains delicate, poorly adhering coatings because the contact cleaning rolls can damage or even remove the delicate coating. Thus, for those webs having delicate coatings, the contact cleaning rolls must be removed to allow the web to pass. Further, removal of such contact cleaning rolls also requires that any web to be coated with a delicate coating must be threaded through the entire coating system rather than merely being tacked onto the end of a previous web and automatically fed around the various idler rolls and drive rolls and coating applying and drying stations. Since a typical production coating utilizes many idler rolls, threading of a web through the system is not a simple task.
The space around coating applicators often has a high solvent content. This is because the solvent in the applied coating mixture is volatile to facilitate drying of the deposited coating. Since most volatile solvents used for coating are also flammable, the regions near coater devices can be explosive. Contact cleaning rolls normally occupy a large volume of space and therefore require extensive floor space. Because electric drive systems are conventionally used to operate the contact cleaning rolls, safety requirements dictated that the cleaning rolls be located outside of coating stations utilizing flammable solvents. This separation between the cleaning rolls and the coating stations increased the likelihood that undesirable contaminates would deposit on the substrate to be coated in the separation space between the cleaning station and the coating station. Such arrangements also increased the footprint of coating systems.
U.S. Pat. No. 5,855,037 to Wieloch et al., issued Jan. 5, 1999xe2x80x94A contact cleaner roll cleaning system is disclosed including a frame to support the system relative to a movable web having a first major surface and a second major surface on opposite sides of the web, at least a first rotatable contact cleaner roll supported on the frame disposed for rolling contact with the first major surface, an activatable web transporting device adapted to transport or interrupt the transport of the web past the first rotatable contact cleaner roll, and a first indexing device adapted to roll the first rotatable contact cleaner roll against the first major surface in a first direction while the transport of the web past the first rotatable contact cleaner roll is interrupted This system is used to clean coated and uncoated webs.
U.S. Pat. No. 5,685,043 to LaManna et al., issued Nov. 11, 1997xe2x80x94A system is disclosed in which a contact cleaning cylinder is brought into moving synchronous contact with the surface of a cylindrical member to be cleaned to clean the surface.
U.S. Pat. No. 5,251,348 to Corrado et al, issued Oct. 12, 1993xe2x80x94A contact cleaner roll cleaning system is described which includes a frame supporting the system relative to a moving web, a contact cleaner roll turret on the frame, and a roll cleaner on the frame. The turret supports two or more rotatable contact cleaner rolls, an active roll in rolling contact with the web, and an idle roll out of contact with the web for cleaning. The idle roll is kept rotating while it is idle and being cleaned. The turret is rotatable to sequentially put the cleaner rolls into and out of contact with the web. The roll cleaner includes an absorbent cleaning material mounted adjacent to the idle roll for placement against it and movement lengthwise along it to wipe it clean. Spindles advance the cleaning material between wipings of the idle roll, and a liquid delivery system keeps the cleaning material wet.
U.S. Pat. No. 5,275,104 to Corrado et al, issued Jan. 4, 1994xe2x80x94Apparatus is disclosed for cleaning a rotating process roll includes cleaning material supply and take-up rolls and a compliant touch roll, all mounted on a carriage adjacent to a process roll. Touch roll and cleaning material are movable by air cylinders into and out of contact with the process roll. The touch roll is rotatable in one direction only with the take-up roll. A drive motor winds the take-up roll to incrementally and uniformly advance the cleaning material over the touch roll. Period and frequency of the cleaning cycle and sub-cycles are variable by microprocessor control. Supply roll and take-up roll are supported in retractable gudgeons for easy mounting and removal.
EPC Patent Application EP 0 756 215 A2, filed Jul. 24, 1996, published Jan. 29, 1997xe2x80x94A contact cleaner roll cleaning system is disclosed, which includes a frame (12) to support the system relative to a moving web (10) having a first major surface and a second major surface, a first rotatable contact cleaner roll (74) supported on the frame disposed for rolling contact with the first major surface of the web, a second rotatable contact cleaner roll (80) supported on the frame disposed for rolling contact with the second major surface of the web, the second rotatable contact cleaner roll having an axis parallel to the axis of the first rotatable contact cleaner roll, the first contact cleaner roll and the second contact cleaner roll being positioned on the frame to support and guide the moving web in a substantially xe2x80x9cSxe2x80x9d shaped path.
Thus, there is a need for a system to produce high quality web cleaning systems which produce higher yields by more effectively removing dirt particles from devices such as coated or uncoated flexible web electrostatographic imaging members.
It is, therefore, an object of the present invention to provide an improved cleaning system which overcomes the above-noted deficiencies.
It is another object of this invention to provide a cleaning system that facilitates coating of a variety of webs, some of which carry durable, strongly adhering coatings and some of which carry delicate, poorly adhering coatings.
It is still another object of this invention to provide a cleaning system which can be positioned closer to cleaning stations.
It is yet another object of this invention to provide a cleaning system that may be utilized in an explosive environment.
It is another object of this invention to provide a cleaning system which reduces the likelihood of deposition of dirt particles between cleaning and coating.
It is still another object of this invention to provide a cleaning system which controls contamination in web cleaning environments where flammable solvents are used to form coatings.
It is yet another object of this invention to provide a cleaning system that reduces the number of idler and other types of guide rolls which accumulate static charge that attract undesirable particles which ultimately transfer to a web being coated.
It is still another object advantage of this invention to provide a cleaning system that provides the option for a web to bypass contact cleaning rolls without contacting the rolls, or to be cleaned by contacting the contact cleaning rolls without a major web path change.
It is another object of this invention to provide a cleaning system that has a smaller footprint.
It is yet another object of this invention to provide a cleaning system that may be used in an explosive atmosphere where other cleaning systems cannot be located.
The foregoing objects and others are accomplished in accordance with this invention by providing a contact cleaner roll cleaning system comprising
a stationary frame,
a rotatable frame, the rotatable frame being rotatable about an axis while supported by the stationary frame, the rotatable frame supporting
a first contact cleaning roll that is rotatable about an axis, the first contact cleaning roll being spaced from and parallel to the axis of the rotatable frame, and
a second contact cleaning roll that is rotatable about an axis, the second contact cleaning roll being spaced from the first contact cleaning roll and parallel to both the axis of the rotatable frame and the axis of the first contact cleaning roll, and
a web transport device disposed to feed a web along a predetermined path between the first contact cleaning roll and the second contact cleaning roll, the web having a first major surface and a second major surface on the opposite sides of the web, the major surfaces being parallel to the axes of the first and second cleaning rolls when fed between the first contact cleaning roll and the second contact cleaning roll.
The contact cleaner roll cleaning system of this invention also includes
providing a first contact cleaning roll spaced from and parallel to a second contact cleaning roll to form an opening between the rolls,
transporting a web in a straight path through the opening between the rolls, the web having a first major surface and a second major surface on the opposite sides of the web, and
simultaneously transporting the first contact cleaning roll and second contact cleaning roll through different arc shaped paths which lie in a common circle whereby the first contact cleaning roll and second contact cleaning roll each separately contact and alter the path of the web.